Apparatus for forming and filling a container

ABSTRACT

An injection device for simultaneously forming and filling a container by injecting a pressurized liquid in a preform. The device includes a molding cavity, a pressurized liquid source and an injection nozzle in fluidic communication with the pressurized liquid source. The injection nozzle is arranged to be placed in fluidic communication with a preform in the molding cavity. A liquid injection circuit is defined by the injection nozzle, the pressurized liquid source and the preform. Also provided is a volume measuring feature for measuring the volume of liquid injected in the preform from the pressurized liquid source and a pressure measuring feature for measuring the pressure in the liquid injection circuit.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 16/077,280, filed Aug. 10, 2018, the entire contents of which areherein incorporated by reference.

BACKGROUND 1. Field of the Invention

The present invention relates to a method for simultaneously forming andfilling a container by injecting a pressurized liquid in a preform.

The invention also relates to an injection device for simultaneouslyforming and filling a container by injecting a pressurized liquid in apreform according to such a method.

The invention relates to the field, known as hydroforming, of formingcontainers from a preform using an incompressible liquid to expand thepreform.

In the application, “liquid” has a physical meaning. It designates anyincompressible and able to flow medium. The liquid can have a lowviscosity (like water or alcohol), a medium viscosity (like edible oilor soup), or a high viscosity (liquid detergent, soap, shampoo, ketchup,mustard). The liquid can be homogeneous or not homogeneous (includingfruit pulp or bits of foodstuff), it can be Newtonian or non-Newtonian.It is not limited to foodstuff. The incompressible liquid may be forexample water, or other beverages, foodstuff such as ketchup,mayonnaise, edible oil, yogurts, home or personal care products, medicalfluids, fuels, hydraulic oil, operating fluids, and the like.

2. Description of Related Technology

In the field of hydroforming, it is known to inject, using an injectiondevice, the incompressible liquid in a heated preform made of plasticmaterial at a pressure which is adapted to urge the wall of the preformagainst the wall of the molding cavity such that the preform is deformedand acquires the shape of the molding cavity and of the container to beproduced.

However, it is also known that this pressure level is not sufficient tocompletely shape the preform into the container, meaning that, with thepressure applied to the preform, the preform acquires a shape which isnot exactly the shape of the molding cavity and that an extradeformation is needed to completely urge the wall of the preform againstthe wall of the molding cavity. It is in particular the case whenembossed letters or logos must be reproduced on the external surface ofthe container wall, or when the wall has ridges. Shapes having locally avery small radius of curvature are very difficult to obtain.

To this end, after the injection of liquid at a first pressure, a secondpressure greater than the first pressure, is applied to the preformduring a short time in order to create a pressure peak inside thepreform, the pressure peak being arranged to finalize the shaping of thepreform into a the container.

One known method for applying the pressure peak is to use the hydraulichammer effect obtained by injecting a liquid in a solid cavity. Indeed,at the end of the injection, the almost shaped container is relativelysolid and a hydraulic hammer effect can be obtained when the liquidinjection is stopped.

However, the pressure reached by with the hydraulic hammer effect ishardly controlled and may be insufficient to fully expand the containeror may be too high. In the latter case, very important mechanicalefforts are applied on the injection device which can damage or cause apremature wear of the injection device. Alternatively, the injectiondevice has to be adapted to sustain the mechanical efforts due to thehydraulic hammer effect, which is not cost effective.

Furthermore, if the pressure peak is not controlled, the shape of thecontainers can vary from one container to the next, which iscontradictory with the need of a fully reproducible process.

Additionally, the inventors have discovered that, when the injectiondevice comprises a movable piston, controlling the course of the piston,i.e. the distance by which the piston is moved, is not an appropriatecontrol to obtain a reproducible process. Indeed, the course of thepiston may not be the same to obtain an identical container from apreform to the next. This phenomenon can be for example explained by thepresence of air in the injected liquid, said air being more or lesscompressed during the movement of the piston, thereby modifying thedistance by which the piston has to be moved to obtain the same pressurein the container and to fully expand the container.

EP 2823948 discloses a station for forming a container form a preform,comprising a main body including a preform seat adapted to receive saidpreform and an injection assembly, said injection assembly comprising aninjection nozzle and an injection device. The injection assemblycomprises maintaining means able to sustain high pressures of liquidflowing in the injection assembly.

US 2015/075119 describes a method of blowing and filling a containerfrom a preform inside a filling and forming apparatus that comprises amold and a pressurized liquid injection circuit able to inject a liquidunder pressure inside the preform when the preform is placed inside themold, the method comprising:

placing a preform inside the mold:

stretching the preform placed within the mold;

starting an injection phase comprising injecting a predetermined volumeof liquid through the liquid injection circuit into the preform;

stopping the injection phase by stopping the injection of the liquidthrough the liquid injection circuit into the preform, creating anoverpressure of liquid within the liquid injection circuit; and

releasing the overpressure of liquid within the liquid injection circuitbefore the blown and filled container is released from the mold in orderto evacuate or discharge the overpressure from the pressurized liquidinjection circuit to avoid repeated stresses on components that are inconnection with this circuit.

US 2014/205707 discloses a device for delivering a predetermined volumeof beverage into a thermoplastic container formed from a heated preform,the preform being positioned in a mold, comprising an injector forinjecting at least some beverage into a recess in the preform so as topromote expansion of the preform inside the mold, the mold defining theshape of the container, a member for longitudinally displacing a stretchrod over a given period and for longitudinally elongating the heatedpreform, the stretch rod being immobile at the end of the given period,and a member for ensuring that a volume of beverage greater than apredefined fraction of the predetermined volume is present in the recessat the end of the given period in order to increase crystallinity of thecontainer at the end of its expansion.

One of the aims of the invention is to overcome the above-mentionedproblems by proposing a method wherein the pressure peak applied to theliquid can be controlled and wherein the shape of the producedcontainers is identical from one container to the next.

SUMMARY OF THE INVENTION

To this end, the invention relates to a method for simultaneouslyforming and filling a container by injecting a pressurized liquid in apreform, said container having a container volume, the pressurizedliquid being injected from a pressurized liquid source to the preformalong an liquid injection circuit while the preform is in a moldingcavity defining the shape of the container, the method comprising:

a first injection step, wherein a first predetermined volume of thepressurized liquid is injected into the preform, said predeterminedvolume corresponding to a fraction of the container volume, said firstinjection step causing an expansion of the preform into a firstintermediate container,

wherein the method further comprises:

a second injection step, wherein, once the first predetermined volume ofliquid has been injected, the liquid injection speed is reduced and thepressurized liquid is further injected in the first intermediatecontainer until a predetermined switch pressure in the liquid injectioncircuit is reached, said second injection step causing an expansion ofthe first intermediate container into a second intermediate container,and

a third injection step starting once the predetermined switch pressureis reached, wherein the liquid injection speed is decelerated until theliquid injection is stopped and the second intermediate container hasexpanded up to said shape of the container.

The inventors have discovered that the pressure inside the injectioncircuit starts to significantly increase slightly before the expandingpreform reaches the final shape of the container. The preform expandsradially and axially when the volume of liquid injected inside thepreform increases beyond the initial inner volume of the preform. Anoptional stretch rod can contribute to the axial stretching of thepreform. The inventors have understood that when the wall of theexpanding preform touches the inner surface of the molding cavity, theliquid pressure starts to increase. From that event, for an incrementalincrease of injected liquid volume, the portion of the preform wallhaving to expand for receiving said incremental volume decreases. Inother words, the more the preform wall is urged against the moldingcavity, the more mechanical resistance the preform opposes to the liquidinjection. The phenomenon of hydraulic hammer happens only when thewhole outer surface of the preform is applied in contact with themolding cavity. Such preliminary ramp up of the pressure inside thecircuit is not the hammer effect itself, it is an indication that thehammer effect is likely to arrive soon. However, when a container issimultaneously formed and filled with pressurized liquid, the fillingtime is usually very short. In particular, when the injected liquid iscolder than the vitreous transition temperature of the preform material,the goal is to fill the container as quickly as possible, and thefilling time could be between 0.1 second to 0.5 second, typically about0.2 second. That may be a reason why the state of the art did not reallydetect the difference between the preliminary ramp up pressure and thereal peak pressure due to a well-known hammer effect.

Indeed, the devices disclosed in EP2823948, US 2015/075119 and US2014/205707 are not adapted to control the pressure reached when thewhole surface of the container is urged against the molding cavity.

The maintaining means disclosed in EP2823948 allow firmly maintainingthe injection assembly in the injection position when a high pressure isreached. However, the pressure inside the container is not controlled.

The method described in US 2015/075119 comprises a step wherein anoverpressure is reached and then evacuated. Consequently, the pressureinside the container is not controlled.

The device described in US 2014/0205707 is a filler in which a containeris formed from a preform before being filled with a liquid. It is thennot adapted to simultaneously form and fill a container by injecting apressurized liquid in a preform.

The inventors have additionally discovered that it is possible to takeadvantage of said preliminary increase of pressure by strongly reducingthe injection speed slightly before said preliminary increase ofpressure is likely to happen. The inventors have discovered a surprisingeffect of combining:

a first injection step allowing a full speed injection,

a second injection step reducing the injection speed before the timeperiod where the preliminary increase of pressure is likely to happen,

detecting when the pressure inside the injection circuit reaches apredetermined switch pressure as to immediately switch to a thirdinjection step allowing, before the hammer effect happens, to start theprocess of stopping the injection.

The time where the pressure inside the injection circuit reaches apredetermined switch pressure may strongly vary from a container toanother, depending of numerous factors like outside temperature, airdissolved into the injected liquid, variation of cavity dimensions, sizeof the molding cavity etc. However, the inventors have discovered thatinitiating the process of stopping the injection before the hammereffect happens allows controlling the pressure reached when the wholesurface of the container is urged against the molding cavity. It ispossible to fully master the pressure peak and to obtain at the end ofthe method identical containers in shape and volume. According toanother feature of the method according to the invention, the secondinjection step comprises a survey period during which the liquidinjection speed is constant and the pressure inside the injectioncircuit is measured and compared to said predetermined switch pressure,and the method comprises driving liquid pressurizing means such that theliquid is injected from a starting time and during the first and secondinjection steps according to a main predetermined curve of injectionspeed or injected volume over time, and such that the injected speedfrom a switching time and during said third injection step follows afinal predetermined curve of injection speed or injected volume overtime.

Such “driving according to a predetermined curve of injection speed orinjected volume” may be an open loop control, for example, when thepressurizing means include a piston, a rotating servomotor and arotation/translation converting mechanism. Such “driving according apredetermined curve of injection speed or injected volume” mayalternatively be a closed loop control, using a return signal correlatedto the real injection speed or injected volume, like using a measurementof a piston position. In both alternative, the fact to drive theinjection by controlling the injection speed or injected volume is muchmore stable and secure than driving by controlling the injectedpressure. As illustrated in FIG. 4, the liquid pressure before reachingsaid switch pressure is rather erratic and depends of many factors likethe synchronization of the injecting speed and the stretch rod speed. Inthe present embodiment the pressurizing means are 100% driven by Speedor Volume control (and not pressure control), before and after theswitch of the “curve of injection speed or injected volume over thetime”. According to another feature of the method according to theinvention, the second injection step comprises a decelerating stepwherein the liquid injection speed is decreased until said liquidinjection speed reaches the constant liquid injection speed, saiddecelerating step occurring until a second predetermined volume ofliquid is injected, said second predetermined volume being comprisedbetween the predetermined volume and the container volume.

Having a phase wherein liquid is injected at a constant speed allows aneasier transition between the second and the third injection step. Forexample, the starting point of the final predetermined curve ofinjection speed over time is said constant speed at the time where theliquid pressure reaches said predetermined switch pressure. According toanother feature of the method according to the invention, the methodcomprises a maintaining period extending at an end portion of the thirdstep, the pressure applied in the liquid injection circuit during saidmaintaining period being a setpoint pressure, the predetermined switchpressure corresponding to a fraction of said setpoint pressure.

This fraction is determined in order to be above the pressure reachedduring the erratic phase of the pressure and early enough to allowavoiding the pressure when the hammer effect occurs increasing too muchabove the setpoint pressure.

The maintaining step allows applying the wanted pressure during asufficient time to fully expand the container and make sure that thedetails of the molding cavity, if such a molding cavity is provided, arecorrectly engraved in the container. Setting the predetermined switchpressure as a fraction of the maintaining pressure makes it possible tostop the injection precisely when the maintaining pressure is reachedsuch that the maintaining pressure is properly controlled.

According to another feature of the method according to the invention,the predetermined switch pressure is substantially comprised between 50%and 75% of the setpoint pressure.

The fraction of the setpoint pressure depends on the speed of the liquidinjection at which the pressure inside the injection circuit has toreach said predetermined switch pressure.

According to other features of the method according to the invention:

the pressurized liquid source comprises a pressurizing device comprisinga movable piston, the liquid injection being controlled by the movementof said piston, the liquid injection speed being controlled bycontrolling the speed of the piston; and

the first predetermined volume is detected by monitoring the position ofthe piston.

Monitoring the position of the piston before the third injection stepallows precisely controlling the volume of injected liquid since saidvolume depends from the position of the piston. According to otherfeatures of the method according to the invention:

the first predetermined volume is comprised between 50% and 85% of thecontainer volume, preferably between 70% and 80% of the containervolume, for example about 75% of the container volume;

the first injection step comprises an initial injection phase, whereinthe pressurized liquid is injected at an increasing injection speed, anda constant injection phase, wherein the pressurized liquid is injectedat a constant injection cruise speed, until the predetermined volume isreached;

the increase in the injection speed of the initial injection phase isequal to the highest liquid acceleration possible.

Such highest acceleration possible is determined by the limit of thehardware used for generating the pressure and/or by the load lossesinside the liquid circuit. According to another feature of the methodaccording to the invention, the pressure in the liquid injection circuitis monitored by a pressure sensor placed in said liquid injectioncircuit.

The invention also relates to an injection device for implementing amethod as described above, comprising a molding cavity, a pressurizedliquid source and an injection nozzle in fluidic communication with thepressurized liquid source, said injection nozzle being arranged to beplaced in fluidic communication with a preform in said molding cavity,said injection nozzle defining with said pressurized liquid source andsaid preform a liquid injection circuit, said injection devicecomprising volume measuring means for measuring the volume of liquidinjected in the preform from the pressurized liquid source and pressuremeasuring means for measuring the pressure in the liquid injectioncircuit.

According to other features of the injection device:

the device comprises driving means for driving the pressurized liquidsource, said driving means being connected to said pressure measuringmeans and connected to a software memory including a main curve ofinjection speed over time, and a final curve of injection speed overtime, said driving means being of a closed loop type based on a returnsignal of the measured injected volume and/or of the measured injectionspeed,

the pressurized liquid source comprises a pressurizing device comprisinga piston moved within a piston body by a servo motor, said volumemeasuring means including a sensor of the piston position,

the pressure in the liquid injection circuit is monitored by a pressuresensor placed in said liquid injection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and advantages of the invention will appear upon readingthe following description, given by way of example and made in referenceto the appended drawings, wherein:

Other aspects and advantages of the invention will appear upon readingthe following description, given by way of example and made in referenceto the appended drawings, wherein:

FIG. 1 is a cross-section view on an injection device allowing toimplement the method according to the invention,

FIG. 2 is a cross-section view of the injection device of FIG. 1 at aninitial step of the method,

FIG. 3 is a cross-section view of the injection device of FIG. 1 atduring the method of the invention, and

FIG. 4 is a graph representing the position of the piston over time in amixt line, the speed of the piston over time in a dashed line and thepressure in the injection circuit over time in hard line.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention can be implemented in a regularinjection device adapted for a hydroforming method and havingappropriate control and monitoring means.

An example of such an injection device 1 is shown in FIG. 1. Theinjection device 1 comprises a liquid source 2, a pressurizing device 4and an injection nozzle 6.

The liquid source 2 contains a liquid to be injected in a preform 8 toexpand said preform into a container 10 (FIG. 3). The liquid isadvantageously the end product, i.e. a liquid that is intended to remainin the container 10 to be delivered to a final consumer. As explainedpreviously, the liquid can be of any appropriate nature.

The liquid source 2 is in fluidic communication with the pressurizingdevice 4, for example via appropriate tubing, which is arranged toinject the liquid into the preform 8 through the injection nozzle 6 at acontrollable pressure and speed.

To this end, the pressurizing device 4 is advantageously a piston devicecomprising a movable piston 12 movable inside a piston body 14. Thepiston body 14 comprises a cylindrical wall 16 comprising an inlet 18and an outlet 20 opening into a pressurizing chamber 22 defined by thepiston 12 and the cylindrical wall 16. The liquid source 2 is placed influidic communication with the pressurizing chamber 22 via the inlet 18and the injection nozzle 6 is placed in fluidic communication with thepressurizing chamber 22 via the outlet 20. The movable piston 12 ismovable inside the piston body 14 such that the volume of thepressurizing chamber 22 is variable depending on the position of thepiston 12 in the piston body 14. More particularly, the piston 12 ismovable between a full position, shown in FIG. 1, wherein the piston 12is spaced from the outlet 20 and the volume of the pressurizing chamber22 is the highest, and an injection position, shown in FIG. 3, whereinthe piston 12 is brought closer to the outlet 20 and the volume of thepressurizing chamber is the lowest. The piston 12 moves according to aninjection direction between the full position and the injectionposition, said injection direction being shown by arrow I in FIGS. 2 and3. It should be noted that the piston 12 is in liquid tight contact withthe cylindrical wall 16 of the injection body 14 to prevent any liquidleaking past the piston 12 out of the injection chamber 22.

The movement of the piston is actuated by appropriate actuation means,for example comprising an actuation rod 24, attached to the piston 12,and a servomotor 26 arranged to move the actuation rod 24 and the piston12 in translation in the injection direction and in a direction oppositethe injection direction, called the filling direction, as shown by arrowF in FIG. 1.

The injection nozzle 6 comprises a nozzle body 28 defining a nozzlechamber 30 placing in fluidic communication an inlet 32 with an outlet34. The inlet 32 is placed in fluidic communication with the outlet 20of the pressurizing device 4 via appropriate tubing. The outlet 34 isarranged to be placed in fluidic communication with the inner volume ofthe preform 8 in a liquid tight manner, as shown in FIGS. 2 and 3.

It should be noted that the injection nozzle 6 can be movable between aretracted position (FIG. 1), wherein a preform 8 can be placed under theoutlet 34 and a container 10 can be retrieved from under the outlet 34,and an injection position (FIGS. 2 and 3), wherein the outlet 34 isplaced in fluidic communication with the inner volume of the preform 8.

A seal pin 36 extends in the nozzle chamber 30 and is movable in saidnozzle chamber 30 between a sealing position (FIGS. 1 and 2), wherein asealing end 38 of the seal pin 36 cooperates with a complementaryportion 40 of the nozzle chamber 30 in a fluid tight manner to preventliquid present in the nozzle chamber 30 to flow through the outlet 34,and a opened position (FIG. 3), wherein the sealing end 38 of the sealpin 36 is spaced from the complementary portion 40 such that liquid canflow through the outlet 34. By complementary portion 40, it is meantthat a part of the nozzle chamber 30 has a shape complementary to theshape of the sealing end 38 of the seal pin 36. This complementaryportion 40 extends for example in the immediate vicinity of the outlet34. The movement of the seal pin 36 is for example controlled by anactuation piston 42 placed in an upper chamber 44 of the injectionnozzle 6 and attached to the seal pin 36. In a known manner, by using anactuation fluid, for example air, in the upper chamber 44, it ispossible move the seal pin 36 between its sealing position and itsclosed position.

The seal pin 36 can be hollow to receive a stretch rod 46 extendingthrough the seal pin 36 along an injection axis A. In a known manner,the stretch rod 46 is movable in translation through the seal pin 36 andthrough the outlet 34 to assist in the axial expansion of the preform 8as will be described subsequently. The movement of the stretch rod 46 iscontrolled by appropriate actuation means (not shown), such as a servomotor or magnetic means or other means.

The injection device 1 further comprises a control unit 48 arranged tocontrol the actuation means of the injection device to control andsynchronize the movements of the movable piston 12, of the seal pin 36and of the stretch rod 46.

The injection device 1 further comprises sensor means that will bedescribed subsequently, in conjunction with the method of the invention.

The injection device 1 described above can be used with a mold 50defining a molding cavity 52 having a shape complementary to the shapeof the container 10 to be produced. As known per se, the mold 50 isarranged to receive the preform 8 such that the inner volume of saidpreform 8 remains accessible to be placed in fluidic communication withthe outlet 34.

A method for simultaneously forming and filling a container 10 byinjecting a pressurized liquid in a preform 8 will now be described,with more particular reference to FIG. 4. The method is implemented inan injection device 1 as described above, wherein the space comprisingthe pressurizing chamber 22, which forms a pressurized liquid source,the tubing connecting the outlet 20 of the pressurizing chamber 22 tothe inlet 32 of the nozzle chamber 30, the nozzle chamber 30, the outlet34 and the inner volume of the preform 8 is referred to as the liquidinjection circuit 54.

First, a heated preform 8 is placed in the molding cavity 52 of the mold50 as shown in FIG. 1. By heated, it is meant that the preform 8, forexample made of PET (polyethylene terephthalate), is heated above itsglass transition temperature such that the preform 8 is in a malleablestate in the molding cavity 52.

Next, the injection nozzle 6 is placed in its injection position, asshown in FIG. 2, such that the outlet 34 is placed in fluidcommunication with the inner volume of the preform 8.

At this stage, the seal pin 36 is in its sealing position and preventsliquid from flowing though the outlet 34. It should be noted that inthis position, the liquid injection circuit 54 is filled with liquidcoming from the liquid source 2 and pressurized by the movable piston12. In order to do so, the movable piston 12 is moved in the fillingdirection F from its injection position such that liquid is drawn fromthe liquid source 2 into the liquid injection circuit 54 and the movablepiston 12 is then moved in the injection direction I to pressurize theliquid while the seal pin 36 is in its sealing position. A non-returnvalve placed in the tube between the liquid source 2 and thepressurizing chamber 22 for example prevents liquid to return to theliquid source 2 during this operation. By pressurizing, it is meant thatthe liquid is brought to a pressure above the atmospheric temperature.For example, just before the opening of the seal pin 36, the pressurecould be between 1 and 2 bar.

Liquid is then injected in the preform 8 by moving the seal pin 36 toits injection position and by moving the movable piston 12 in theinjection direction I, as shown in FIG. 3, which expands the preform 8and urges the wall of the preform 8 towards the wall of the moldingcavity 52 as represented by the arrows in the container 10 of FIG. 3.

Before and/or during this injection of liquid, the stretch rod 46 can bemoved to contact the bottom of the preform 8 and to exert a stretchingforce on said bottom such that the preform is expanded along theinjection axis A, as known per se.

The liquid injection comprises several steps which will now bedescribed.

In FIG. 4, the position of the piston 12 is represented in mixt lines;the speed of the piston 12 is represented in dashed line and reports toan “S” vertical axis; and the pressure of the liquid inside theinjection circuit 54 (visible in FIG. 0.1) is represented in integralline and reports to the “P” vertical axis.

At the start of the injection, i.e. when the seal pin 36 is moved to itsinjection position, a first injection step starts wherein the preform 8is expanded up to a first intermediate container having a volumecorresponding to a fraction of the volume of the final container 10 tobe produced, also called container volume. In other words, the firstintermediate container is a not fully expanded container. To form thisfirst intermediate container, a first predetermined volume of liquid isinjected in the preform 8 by moving the injection piston 12 in theinjection direction. Said start of the injection is represented by arrowt₁ in FIG. 1.

The first predetermined volume of liquid is equal to a fraction of thecontainer volume, for example comprised between 40% and 90% of thecontainer volume, preferably comprised between 50% and 75% of thecontainer volume. According to an embodiment, the predetermined volumeis 75% of the container volume. According to another embodiment, thepredetermined volume is 50% of the container volume.

The injected volume can be controlled by controlling the position of themovable piston 12 in the piston body 14. Indeed, the distance by whichthe piston 12 is moved in the injection direction I in the piston body14 while the seal pin 36 is in the injection position, corresponds to anamount of liquid injected in the preform 8. Consequently, controllingthe position of the piston 12 allows an accurate control of the volumeof pressurized liquid injected in the preform 8. Consequently, theinjection device comprises means to monitor and control the position ofthe piston 12 in the piston body 14. Such means are for example coupledto the servomotor 26 driving the piston 12 and to the control unit 48.

These means are arranged such that when a predetermined position of thepiston 12 corresponding to the predetermined volume of pressurizedliquid injected in the preform 8 is reached, a second injection stepbegins wherein the behaviour of the piston 12 changes, as will bedescribed subsequently.

The predetermined position of the piston 12 corresponding to thepredetermined volume of pressurized liquid injected in the preform 8 isrepresented by arrow t₂ in FIG. 4. One can see that, between time t₁ andtime t₂, the value of the position of the piston has increased relativeto the initial value of the position before time t₁. The initial valuecorresponds to the position of the piston 12 in the full position shownin FIG. 1 and the value of the position increases as the piston 12 ismoved toward the injection position, i.e. as the piston 12 is broughtcloser to the outlet 20 of the piston body 14. This means that betweentime t₁ and time t₂, the piston 12 has moved from its full position toan intermediate position between the full position and the injectionposition, said intermediate position being reached when thepredetermined volume of pressurized liquid has been injected in thepreform 8.

The method also involves monitoring and controlling the speed ofdisplacement of the piston 12 in the piston body via appropriate meansalso coupled to the servomotor 26 and to the control unit. The speed ofthe piston is shown in dashed lines in FIG. 4.

As can be seen in FIG. 4, during the first injection step, i.e. at atime t₁′ between time t₁ and time t₂, the speed of the piston 12 firstincreases rapidly and then is constant between time t₁′ and time t₂where the intermediate position of the piston 12 is reached.

The increase in the speed of the piston 12 corresponds to an initialinjection phase during which the movement of the piston 12 isaccelerated to rapidly reach a cruise speed Sc. The acceleration isarranged to be the most important possible with the injection device 1of the invention. This means that the increase in the injection speed ofthe initial injection phase is equal to the highest liquid accelerationpossible in the injection circuit, meaning that the increase of theinjecting liquid flow speed is the maximum increase that can begenerated by the actuator of the piston 12. For example, if the actuatoris an electric motor or a servo motor, the maximum is determined by themaximum current just before the security cut off. In other words, theaim of the initial phase is to reach the cruise speed Sc as fast aspossible, such that the piston 12 moves at the cruise speed Sc for mostof the first injection step. The acceleration is for example around 1Gor 2G depending on the energy that can be consumed for this operation.

Moving the piston 12 at a constant speed equal to the cruise speed Scallows a better control of the synchronization of the movement of thepiston 12 with the movement of the stretch rod and or with other partsof the injection device. Furthermore, the movement at a constant speedeases the detection of the intermediate position of the piston 12, i.e.the determination of time t₂.

At time t₂, a second injection step begins during which the pressureinside the liquid injection circuit 54 is monitored such that apredetermined switch pressure Pp inside the liquid injection circuit 54can be detected at time t₃, where a third injection step begins as willbe described subsequently.

The predetermined switch pressure Pp to be detected is equal to afraction of a setpoint pressure Ps that has to be applied to thecontainer at the end of the method and arranged to fully and properlyimpart the shape of the molding cavity on the container 10. Such asetpoint pressure Ps allows obtaining a completely formed container inparticular when local details, such a ridges or ribs, has to beimprinted in the container. The setpoint pressure Ps substantiallycorresponds to the pressure peak that has to be applied to the containerand which is greater than the pressure applied to the preform during thefirst injection step and at the beginning of the second injection step,as can be seen in FIG. 4, wherein the pressure inside the liquidinjection circuit 54 is shown in hard line. As an example, the pressureapplied during the first injection step and at the beginning of thefirst step is around 1 to 2 bar and the setpoint pressure Ps may bearound 40 bar.

As explained previously, the predetermined switch pressure Pp is afraction of said setpoint pressure Ps, which is chosen depending on aspeed of the piston 12 during the second injection step and at which thepredetermined switch pressure Pp is to be detected as will now beexplained.

During the second injection step, the speed of the piston 12 isdecreased until it reaches a detection speed Sd inferior to the cruisespeed Sc. To this end, the second injection step comprises a step ofdecelerating the piston 12 until it reaches the detection speed Sd attime t₂′ and then maintaining the speed of the piston 12 at a constantspeed equal to the detection speed Sd until the predetermined switchpressure Pp is reached at time t₃.

The deceleration is also the highest deceleration that the piston can besubjected to with the injection device such that the detection speed Sdis reached as fast as possible. In fact, the detection speed has to bereached at a time when the pressure inside the liquid injection circuit54 starts to increase rapidly, i.e. when the volume of liquid injectedinside the container is close to the container volume that has to bereached. Indeed, during the second injection step, the firstintermediate container is further expanded into a second intermediatecontainer having a volume greater than the volume of the firstintermediate container and close to the container volume. Before thevolume of the second intermediate container is reached, the expansion ofthe container is reduced and, as liquid is further injected into thecontainer, the pressure raises rapidly inside the liquid injectioncircuit 54.

The aim of the invention is to detect the predetermined switch pressurePp in order to modify the behavior of the piston when said predeterminepressure is reached, as will be described subsequently. However, thepredetermined switch pressure is located in this rapid pressure rise asshown in FIG. 4, which makes it difficult to detect. One way of beingable to detect this predetermined switch pressure Pp is to reduce thespeed of the piston 12 during the second injection step such that thepressure rise is not too steep. Indeed, if the speed of the piston wasto be maintained at the cruise speed Sc, the pressure rise would be verysteep, i.e. almost vertical in the graph of FIG. 4, and the detection ofthe predetermined switch pressure would not be possible, whereas, whenthe piston 12 moves at the detection speed Sd, which is inferior to thecruise speed Sc, and which is constant once it is reached, thepredetermined switch pressure is detectable. The predetermined switchpressure can be detected by a pressure sensor placed in the liquidinjection circuit 54 or by monitoring a current signal of the motordriving the movable piston, for example the servomotor 26.

The increase of pressure inside the liquid injection circuit starts whenthe intermediate container has a volume substantially comprised between90% and 95% of the container volume. Consequently, the deceleration ofthe piston 12 at the beginning of the second injection step is arrangedsuch that the detection speed Sd is reached when the volume of liquidinjected in the intermediate container is substantially comprisedbetween 90% and 95% of the container volume, for example when saidvolume is equal to 94% of the container volume.

The piston 12 is then moved at a constant speed equal to the detectionspeed Sd until the predetermined switch pressure is detected at time t₃,where the third injection step begins.

When the detection speed Sd is substantially equal to 100 mm/s, thepredetermined switch pressure Pp is set to be equal to 50% of thesetpoint pressure Ps. When the detection speed is substantially equal to50 mm/s, the predetermined switch pressure Pp is set to be equal to 75%of the setpoint pressure Ps. This is because, once the predeterminedswitch pressure Pp is reached, the injection device has to be able tofurther decrease the speed of the piston rapidly during the thirdinjection step to master the pressure peak that will occur during thisthird injection step.

As mentioned above, at time t₃, the third injection step begins and thespeed of the piston is further decreased until said speed is equal to 0and the piston no longer moves in the injection position, i.e. until thepiston reaches the injection position shown in FIG. 3. In this position,the liquid injection is stopped, meaning that no further amount ofliquid enters the container 10.

A hydraulic hammer effect then occurs wherein the pressure exceeds thesetpoint pressure Ps. However, thanks to the method of the invention,this hammer effect is not too important and can be sustained by theinjection device, without the need of a particular oversizing of theinjection device. After the hydraulic hammer, the pressure then settlesto the setpoint pressure Ps, at which the container is completelyapplied against the wall of the molding cavity 52 and at which the shapeof the container is properly defined. Consequently, at the end of thethird step, the second intermediate container has expanded into thefinal container.

The principle of the invention is therefore to control the applicationof the setpoint pressure Ps by monitoring the pressure of the liquidinside the liquid injection circuit 54 at the end of the expansion ofthe container, rather than by monitoring the position of the piston, asit is conventionally done. By doing so, one makes sure that the setpointpressure Ps is applied to the container, which is not the case when theposition of the piston is monitored since the position of the pistonwhen the setpoint pressure is reached can vary from one container to thenext, for example depending on the amount of air that is compressed inthe liquid injection circuit 54 and which can vary from one container tothe next.

Consequently, the method of the invention makes it possible to apply thesame setpoint pressure Pp to all the containers produced by theinjection device. The containers produced by the method are thereforeuniform and the method is fully reproducible.

According to an embodiment, the method of the invention furthercomprises a maintaining step after the third injection step, saidmaintaining step starting at time t₄. During this maintaining step, thepiston is maintained in the injection position such that the setpointpressure is applied in the liquid injection circuit 54 and in thecontainer for a predetermined amount of time, ending at time t₅. Thismaintaining step allows applying the wanted pressure during a sufficienttime to fully expand the container and make sure that the details of themolding cavity, if such a molding cavity is provided, are correctlyengraved in the container.

Once the maintaining step is over, the seal pin 36 is moved back in itssealing position and the formed container can be retrieved from the mold50.

The method can then be applied to a subsequent preform 8.

The method of the invention has been described in conjunction with theuse of a piston to pressurize and inject the liquid, the speed of thepiston allowing to control the speed of liquid injection. However, thepressurized liquid source could also be formed by a pump. In this case,the liquid injection speed and the injected liquid volume are controlledby controlling the pump. The method remains the same, the control of thevolume being replaced by the control of the pressure once the containeris almost fully expanded in order to master the pressure peak to beapplied to the container.

I/We claim:
 1. An injection device for simultaneously forming andfilling a container by injecting a pressurized liquid in a preform, thedevice comprising a molding cavity, a pressurized liquid source and aninjection nozzle in fluidic communication with the pressurized liquidsource, the injection nozzle being arranged to be placed in fluidiccommunication with a preform in the molding cavity, the injection nozzledefining with the pressurized liquid source and the preform a liquidinjection circuit, the injection device including a volume measuringmeans for measuring the volume of liquid injected in the preform fromthe pressurized liquid source and pressure measuring means for measuringthe pressure in the liquid injection circuit.
 2. The injection deviceaccording to claim 1, further comprising driving means for driving thepressurized liquid source, the driving means being connected to thepressure measuring means and connected to a software memory including amain curve of injection speed over time, and a final curve of injectionspeed over time, the driving means being of a closed loop type based ona return signal of the measured injected volume and/or of the measuredinjection speed.
 3. The injection device according to claim 1, whereinthe pressurized liquid source comprises a pressurizing device having apiston, a piston body and a servo motor, the piston being moveablewithin the piston body by the servo motor, the volume measuring meansincluding a sensor of the piston position.
 4. The injection deviceaccording to claim 1, wherein the pressure measuring means includes apressure sensor placed in the liquid injection circuit.